The invention is directed to an expansion dowel having an expansion sleeve which comprises longitudinal slots open towards the setting end as well as a bore tapering inwardly towards the setting or leading end, wherein an expanding member is provided tapering inwardly at least partially towards the setting end and is inserted into the bore of the expansion sleeve and the expanding member has a recess open toward the setting end for purposes of partial radial deformation.
Expansion dowels of the above-mentioned type are in extensive use. They are used in rock, concrete, masonry and other receiving materials of a similar type. As a rule the expansion dowels are installed in such a way, that a receiving aperture is fabricated in the receiving material in a first work step and after inserting the expansion dowel into this receiving aperture, the expansion sleeve is expanded by advancing an expanding member in the setting direction. A setting tool in the form of a dome is used for the expansion process, which in connection with an appropriate driving appliance applies blows to the expanding member.
In order to assure the expansion process and also to facilitate the work of the operating personnel, one proceeds in a way that the expanding member is advanced in the setting direction by means of the setting tool, until it has reached a specific depth inside the expansion sleeve. This depth can be determined only by means of the setting tool, so that the setting tools used here can for instance be provided with an appropriate marking, which indicates to the operator, when the expansion process can be discontinued. Instead of such a marking, a stop shoulder, for instance in the form of a collar, is used at the setting tool in a preferred manner as additional help for the operator, so that apart from a pure visual control an additional positive control by travel limitation of the setting tool is established.
The above-mentioned setting method has the disdvantage, that on the one hand the expanding member covers always the same distance and therefore always widens the expansion sleeve in the same way, independently of the external forces acting upon the expansion sleeve counter to the expansion force. Herein the forces acting upon the expansion sleeve are a function of different factors, for instance in particular of the nature of the receiving material and the diameter or the accuracy of the receiving aperture in the receiving material. Thus it can occur that the constant travel with which the expanding member is advanced inside of the expansion sleeve results in inadequate anchoring values in one extreme case and in another extreme case damages the receiving material due to overstressing, so that this case also results in inadequate anchoring values.
In order to eliminate the above-mentioned disadvantages it is proposed in the DE-PS 26 17 191, to provide an expansion dowel with an expanding member comprising radially deformable zones. In this known expanding dowel the expansion member is also advanced inside of the expansion sleeve always covering the same distance, wherein however depending upon the magnitude of the external forces the deformable zones of the expanding member are being deformed to a greater or lesser extent. This eliminates damage to the receiving material caused by overload and also results in lower anchoring values. However in the known expansion dowel the design of the deformable zones provided in the expanding member has a disadvantageous effect. The proposed design in the shape of webs or slots, if need be connected with a recess, does not permit controlling the deformation behavior. Thus none of the proposed expanding members can produce adequate expansion forces because of the loss of stiffness. A considerable reduction of the anchoring values produced in this known expansion dowel is thus the consequence.